The present invention relates generally to semiconductor fabrication and, more particularly, to methods and systems for controlling the temperature of the surface of the belt pad and the slurry temperature in linear chemical mechanical planarization (CMP).
Generally speaking, linear CMP processes involve a wafer being rotated under pressure against the surface of a belt pad in the presence of a slurry, which contains a mixture of abrasive material and chemicals. The slurry is typically provided by a slurry bar, which is disposed above the belt pad and has a plurality of nozzles. In operation, the nozzles dispense slurry onto the surface of the belt pad. During planarization, the removal rate across the surface of the wafer is influenced by the temperature profile across the belt pad. For example, the removal rate at the edges of the wafer tends to be less than the removal rate at the center of the wafer because the temperature at the edges of the belt pad tends to be lower than at the center of the belt pad, especially at the start of a CMP operation. In light of this problem, which is sometimes referred to as the “wafer effect,” it is often necessary to run a number of dummy wafers before a stable removal rate and acceptable within-wafer nonuniformity (WIWNU) are obtained and the processing of actual process wafers can begin.
In view of the foregoing, there is a need for a method that allows a greater degree of control over the temperature profile across the surface of a belt pad.